Heart valve replacement is required when a patient's heart valve becomes diseased or damaged. Surgically implanted heart valve prostheses have extended the life expectancy of many patients with defective heart valves. Such prostheses can be either mechanical or biological (tissue valves), stented or stentless, and may be implanted into an aortic, mitral, tricuspid, or pulmonary position.
Stented heart valves made from flexible material or from materials that exhibit shape memory characteristics promise less complicated and faster valve implantation procedures. The stents supporting the heart valves are generally cylindrical in shape and are structured to be crimped so as to reduce their size for delivery to a target site. The stents may be either self-expanding or non self-expanding. Self-expanding stents may be formed from any suitable shape memory material, such as Nitinol. Non self-expanding stents are typically expanded via an inflation means or mechanical expansion means. Stented heart valves are sometimes referred to as suture-less valves because they may be implanted and secured into the annulus without the use of sutures.
As appreciated by those of ordinary skill in the art, it is desirable to crimp or otherwise radially compress the stent in a substantially uniform manner to minimize the variation in pressures applied to the stent. Such pressure variations may lead to deformation of the stent, which may reduce the ability of the stent to securely maintain the heart valve at the target location. Thus, if a stent is crimped in a non-uniform manner, it is typically either re-crimped or thrown away. Re-crimping of stents is not desirable because the repeated application of force on the stent may cause fatigue or weakening of the stent structure. Disposing of poorly crimped stents is also not desirable due to the increased costs associated with the waste. This is especially true with stented heart valves because the stent and the heart valve are attached together and must be disposed of as a single unit.
A number of different strategies have been used to repair or replace a defective heart valve with stented replacement valves. Surgical valve repair or replacement surgery involves a gross thoracotomy, usually in the form of a median sternotomy. In this procedure, a saw or other cutting instrument is used to cut the sternum longitudinally and the two opposing halves of the anterior or ventral portion of the rib cage are spread apart. A large opening into the thoracic cavity is thus created, through which the surgeon may directly visualize and operate upon the heart and other thoracic contents. The patient must be placed on cardiopulmonary bypass for the duration of the surgery. Open-chest valve replacement surgery has the benefit of permitting the direct implantation of the replacement valve at its intended target site. For example, the stented replacement valve may be delivered to the target site with a delivery catheter or the like. Once positioned in the desired location, the stent may be re-expanded to secure the replacement heart valve in place by exerting radial forces against the internal walls of the implantation annulus.
Minimally invasive percutaneous valve replacement procedures have emerged as an alternative to open-chest surgery. Unlike open-heart procedures, percutaneous procedures are indirect and involve intravascular catheterization from a vessel, such as femoral, subclavian and the like, to the heart. Because the minimally invasive approach requires only a small incision, it allows for a faster recovery for the patient with less pain and the promise of less bodily trauma. This, in turn, reduces the medical costs and the overall disruption to the life of the patient.
The use of a minimally invasive approach, however, introduces new complexities to surgery. An inherent difficulty in the minimally invasive percutaneous approach is the limited space that is available within the vasculature. Unlike open-heart surgery, minimally invasive heart surgery offers a surgical field that is only as large as the diameter of a blood vessel. Consequently, the introduction of tools and prosthetic devices becomes a great deal more complicated. The device must be dimensioned and configured to permit the device to be introduced into the vasculature, maneuvered therethrough, and positioned at a desired implant location.
In addition to surgical and minimally invasive percutaneous procedures, it is also possible to implant a replacement valve through the apical area of the heart. The apical area of the heart is generally the blunt rounded inferior extremity of the heart formed by the left and right ventricles. In normal healthy humans, the apical area generally lies behind the fifth left intercostal space from the mid-sternal line. The unique anatomical structure of the apical area permits the introduction of various surgical devices and tools into the heart without significant disruption of the natural mechanical and electrical heart function. Because transapical procedures allow direct access to the heart and great vessels through the apex, they are not limited by the size constraints which are presented by percutaneous surgical methods. While access to the heart through the femoral vessels in percutaneous methods are limited to the diameter of the vessel (approximately 8 mm), access to the heart through the apical area is significantly larger (approximately 25 mm). Thus, apical access to the heart permits greater flexibility with respect to the types of devices and surgical methods that may be performed in the heart and great vessels.
Thus, because the transapical approach is different than conventional open-chest and minimally invasive percutaneous approaches, a new system and method for deploying a heart valve using transapical techniques are needed.